In application virtualization, an application is deployed to a client machine in a virtual environment. A virtual environment includes resources that are accessible to the application installed in that environment and includes files, registry keys, and so forth. Virtualization facilitation software intercepts many operating system Application Program Interface (API) calls (such as read request, write request, events, and so forth) that the application makes in the virtual environment. The virtualization facilitation software then redirects the calls to another location. This other location is a managed location that can be sandboxed on the client machine. Accordingly, the installation and operation of the application is isolated from the native environment of the client machine.
The virtualization facilitation software thus provides the illusion to the application installed in the virtual environment that the application is just running on the client machine in its normal environment, and thus the application has no information regarding the existence of such a virtual environment. Likewise, the operating system is also unaware of the virtual environment, but just receives API calls just as the operating system normally would.
This isolation means that an application can be cleanly installed and removed from the client machine, thus facilitating convenient application management. Furthermore, since the installed application is isolated from the native environment, the installed application is also isolated from other applications that might be running on the client machine. Thus, application virtualization permits applications to be more cleanly installed on, run in, and removed from a client machine.
Conventional application virtualization occurs at the process level. All threads of a process running in a virtual environment are also run in the virtual environment. These threads have access to all the virtual resources (such as files, registry keys, and so forth) of their process, but do not have access to virtual resources of other virtual environments. Likewise, threads running within native processes do not have access to any virtual resource in any virtual environment.